氯化铵对马铃薯酪氨酸酶的抑制作用

以马铃薯为材料,采用磷酸盐缓冲液抽提,经硫酸铵沉淀,Sephadex G-100提取酪氨酸酶,研究氯化铵对马铃薯酪氨酸酶催化L-多巴氧化活力的影响。结果表明,氯化铵对马铃薯酪氨酸酶有较强的抑制作用,其抑制马铃薯酪氨酸酶活力下降50%的抑制浓度(IC50)为0.2 mol/L。氯化铵对马铃薯酪氨酸酶的抑制作用表现为可逆非竞争性抑制,抑制常数为4.88 mmol/L。     

TMEM16A, a membrane protein associated with calcium-dependent chloride channel activity

Calcium-dependent chloride channels are required for normal electrolyte and fluid secretion, olfactory perception, and neuronal and smooth muscle excitability. The molecular identity of these membrane proteins is still unclear. Treatment of bronchial epithelial cells with interleukin-4 (IL-4) causes increased calcium-dependent chloride channel activity, presumably by regulating expression of the corresponding genes. We performed a global gene expression analysis to identify membrane proteins that are regulated by IL-4. Transfection of epithelial cells with specific small interfering RNA against each of these proteins shows that TMEM16A, a member of a family of putative plasma membrane proteins with unknown function, is associated with calcium-dependent chloride current, as measured with halide-sensitive fluorescent proteins, short-circuit current, and patch-clamp techniques. Our results indicate that TMEM16A is an intrinsic constituent of the calcium-dependent chloride channel. Identification of a previously unknown family of membrane proteins associated with chloride channel function will improve our understanding of chloride transport physiopathology and allow for the development of pharmacological tools useful for basic research and drug development.     

Regulation of chloride channels by protein kinase C in normal and cystic fibrosis airway epithelia

Apical membrane chloride channels control chloride secretion by airway epithelial cells. Defective regulation of these channels is a prominent characteristic of cystic fibrosis. In normal intact cells, activation of protein kinase C (PKC) by phorbol ester either stimulated or inhibited chloride secretion, depending on the physiological status of the cell. In cell-free membrane patches, PKC also had a dual effect: at a high calcium concentration, PKC inactivated chloride channels; at a low calcium concentration, PKC activated chloride channels. In cystic fibrosis cells, PKC-dependent channel inactivation was normal, but activation was defective. Thus it appears that PKC phosphorylates and regulates two different sites on the channel or on an associated membrane protein, one of which is defective in cystic fibrosis.     

Altered regulation of airway epithelial cell chloride channels in cystic fibrosis

In many epithelial cells the chloride conductance of the apical membrane increases during the stimulation of electrolyte secretion. Single-channel recordings from human airway epithelial cells showed that beta-adrenergic stimulation evoked apical membrane chloride channel activity, but this response was absent in cells from patients with cystic fibrosis (CF). However, when membrane patches were excised from CF cells into media containing sufficient free calcium (approximately 180 nanomolar), chloride channels were activated. The chloride channels of CF cells were similar to those of normal cells as judged by their current-voltage relations, ion selectivity, and kinetic behavior. These findings demonstrate the presence of chloride channels in the apical membranes of CF airway cells. Their regulation by calcium appears to be intact, but cyclic adenosine monophosphate (cAMP)-dependent control of their activity is defective.     

Divalent phosphate electrode

Divalent phosphate ion activities can be measured in dilute aqueous solutions in the physiological pH range (7.0 to 7.5) with a liquid ionexchange membrane electrode system; the organic ion exchanger consists of an amine chloride membrane. Reference solutions may be either aqueous chloride or bicarbonate solutions. An essentially Nernstian slope is obtained.     

Intracellular calcium: its movement during pentylenetetrazole-induced bursting activity

The intracellular calcium concentration in the cytoplasm decreased and the calcium concentration near the cell membrane increased during bursting activity induced by pentylenetetrazole in snail neuron. Incubation in medium containing cobalt chloride or lanthanum chloride did not change this tendency, which suggests that this calcium distribution change is due to the stored calcium in the subcellular structure moving toward the cell membrane.     

氯化钙在提高玉米抗盐性方面的作用

试验用0.5%的氯化钙(CaCl2)溶液浸种,在Na2CO3胁迫下,对玉米的干物重、叶绿素含量、细胞膜透性、根系活力、脯氨酸含量和水势的保护性作用进行研究。结果显示,用CaCl2浸种的玉米在胁迫下的叶绿素含量、细胞膜透性和根系活力的变化程度均小于水浸种,脯氨酸含量、干物重高于水浸种,水势低于水浸种。结果表明,CaCl2浸种提高了三叶期玉米的抗盐能力。     

茶树根系跨膜主动吸收氟的表观特征

为研究茶树根系跨膜主动吸收氟的过程,采用溶液培养法分析了茶树吸收氟的动力学特性,探究了温度、代谢抑制剂和氯离子等因素对茶树根系主动吸收氟的影响。结果表明,浓度吸收试验可用Michaelis-Menten动力学模型拟合,获得动力学参数Vmax=13.9μg·h~(-1)·g~(-1)(根干重,DW),Km=0.59 mmol·L~(-1)。与在25℃培养条件下相比,低温处理(4℃)明显抑制了茶树对氟的吸收,抑制率达到49.75%。代谢抑制剂2,4-Dinitrophenol(2,4-DNP)、叠氮钠(NaN_3)和正钒酸钠(Na_3VO_4)均抑制了茶树根系对氟的吸收过程,而且随着代谢抑制剂处理浓度的增加,茶树根系氟含量和累积量也随之不断减少。在2,4-DNP、叠氮钠和正钒酸钠浓度分别为2、0.2mmol·L~(-1)和0.6 mmol·L~(-1)条件下,茶树根系氟含量分别比对照减少了16.1%、39.1%和20.6%。当营养液中氟和氯浓度均为5 mmol·L~(-1)时,氯离子显著抑制了茶树对氟的吸收,抑制率达到73.1%,存在拮抗作用。从表观上分析,茶树根系对氟的吸收是一个与跨质膜电化学势梯度、代谢能量和载体蛋白有关的主动运输过程。     

A new charge-mosaic membrane from a multiblock copolymer

A charge-mosaic membrane was prepared from a pentablock copolymer of the BABCB type by selectively introducing anion and cation exchange groups into the microseparated phases. The three-layer lamellar structure of the starting pentablock copolymer film was not disturbed by the modifications. The membrane obtained was highly permeable only to sodium chloride in mixed aqueous solutions of sodium chloride and organic species of low molecular weight, such as sucrose. Marked pH-dependent permeabilities were also observed for amino acids.     

DDT: inhibition of sodium chloride tolerance by the blue-green alga Anacystis nidulans

Anacystis nidulans, a freshwater blue-green alga, has been found to lerate sodium chloride (1 percent by weight) and DDT [1,1,1-trichloro-2,2-bis chlorophenyl) ethane] (800 parts per billion) separately, but growth was inhibited in the presence of both compounds. This inhibition was reversed by an increased calcium concentration. It is possible that inhibition of (Na+,K+)-activated adenosine triphosphatase) by DDT causes this species to lose the ability to lerate sodium chloride.     

Activation of apical chloride channels in the gastric oxyntic cell

Oxyntic cells that retain distinct morphological polarity between apical and basolateral membranes were isolated from the gastric mucosa of the amphibian Necturus. Patch-clamp techniques were applied to these cells to identify apical membrane ion channels associated with hydrochloric acid secretion. A single class of voltage-dependent, inwardly rectifying chloride channels was observed in the apical membranes of both resting and stimulated (acid-secreting) oxyntic cells. Stimulation of the cells with dibutyryladenosine 3',5'-monophosphate and isobutylmethylxanthine increased channel open probability and simultaneously increased apical membrane surface area. This chloride channel is probably responsible for electrogenic chloride secretion by the gastric mucosa and may also participate in the fluid- and enzyme-secretory functions of the oxyntic cell, analogous to the chloride channels found in the apical membranes of other exocrine cells.     

氯化胆碱浸种对盐迫下稻种萌发及幼苗生长的影响

为了明确氯化胆碱对NaCl胁迫的缓解作用,以水稻品种隆粳20和粳2837为材料,采用0、200、400、600和800 mg/L浓度的氯化胆碱溶液浸种处理研究氯化胆碱浸种对NaCl胁迫下水稻种子萌发以及幼苗生长的影响。结果表明:盐胁迫下水稻种子的发芽势、发芽率等均显著降低,而根长、芽长等指标随着盐浓度的升高受到不同程度的抑制,试验表明7.5 g/L NaCl抑制率约为50%,因此选取7.5 g/L NaCl溶液作为对不同浓度氯化胆碱浸种后的水稻种子萌发和幼苗胁迫处理的盐浓度。氯化胆碱浸种能明显提高NaCl胁迫下水稻种子的发芽势、发芽率,同时增加根长、芽长等指标,对NaCl胁迫下水稻种子萌发以及幼苗的生长具有明显的缓释作用。由此说明,氯化胆碱浸种可以缓解NaCl胁迫对水稻种子萌发的影响,提高水稻种子的耐盐性。     

Ionic mechanism of cholinergic inhibition in molluscan neurons

Acetylcholine, the inhibitory transmitter to the so-called H-neurons of molluscs, produces its effect by increasing the permeability of the subsynaptic membrane to chloride ions. The change in permeability gives rise to a net influx of this anion, which hyperpolarizes the neuron. The presence of an outward pump of chloride ions is postulated to account for the required electrochemical gradient. The participation of potassium ions in this inhibitory phenomenon was not detected.     

Functional coupling of gamma-aminobutyric acid receptors to chloride channels in brain membranes

gamma-Aminobutyric acid (GABA), the major inhibitory neurotransmitter in mammalian brain, is believed to act by increasing membrane conductance of chloride ions. In this study it was found that GABA agonists increased the uptake of chloride-36 by cell-free membrane preparations from mouse brain. This influx was rapid (less than 5 seconds), and 13 micromolar GABA produced a half-maximal effect. The GABA antagonists (bicuculline and picrotoxin) blocked the effect of GABA, whereas pentobarbital enhanced the action. This may be the first demonstration of functional coupling among GABA and barbiturate receptors and chloride channels in isolated membranes. The technique should facilitate biochemical and pharmacological studies of GABA receptor-effector coupling.     

Apolipoprotein L-I promotes trypanosome lysis by forming pores in lysosomal membranes

Apolipoprotein L-I is the trypanolytic factor of human serum. Here we show that this protein contains a membrane pore-forming domain functionally similar to that of bacterial colicins, flanked by a membrane-addressing domain. In lipid bilayer membranes, apolipoprotein L-I formed anion channels. In Trypanosoma brucei, apolipoprotein L-I was targeted to the lysosomal membrane and triggered depolarization of this membrane, continuous influx of chloride, and subsequent osmotic swelling of the lysosome until the trypanosome lysed.     

The role of chloride transport in postsynaptic inhibition of hippocampal neurons

Hippocampal inhibitory postsynaptic potentials are depolarizing in granule cells but hyperpolarizing in CA3 neurons because the reversal potentials and membrane potentials of these cells differ. Here the hippocampal slice preparation was used to investigate the role of chloride transport in these inhibitory responses. In both cell types, increasing the intracellular chloride concentration by injection shifted the reversal potential of these responses in a positive direction, and blocking the outward transport of chloride with furosemide slowed their recovery from the injection. In addition, hyperpolarizing and depolarizing inhibitory responses and the hyperpolarizing and depolarizing responses to the inhibitory neurotransmitter gamma-aminobutyric acid decreased in the presence of furosemide. These effects of furosemide suggest that the internal chloride activity of an individual hippocampal neuron is regulated by two transport processes, one that accumulates chloride and one that extrudes chloride.     

A C. elegans CLIC-like protein required for intracellular tube formation and maintenance

The Caenorhabditis elegans excretory canal is composed of a single elongated and branched cell that is tunneled by an inner lumen of apical character. Loss of the exc-4 gene causes a cystic enlargement of this intracellular tube. exc-4 encodes a member of the chloride intracellular channel (CLIC) family of proteins. EXC-4 protein localizes to various tubular membranes in distinct cell types, including the lumenal membrane of the excretory tubes. A conserved 55-amino acid domain enables EXC-4 translocation from the cytosol to the lumenal membrane. The tubular architecture of this membrane requires EXC-4 for both its formation and maintenance.     

Cl- channels in CF: lack of activation by protein kinase C and cAMP-dependent protein kinase

Secretory chloride channels can be activated by adenosine 3',5'-monophosphate (cAMP)-dependent protein kinase in normal airway epithelial cells but not in cells from individuals with cystic fibrosis (CF). In excised, inside-out patches of apical membrane of normal human airway cells and airway cells from three patients with CF, the chloride channels exhibited a characteristic outwardly rectifying current-voltage relation and depolarization-induced activation. Channels from normal tissues were activated by both cAMP-dependent protein kinase and protein kinase C. However, chloride channels from CF patients could not be activated by either kinase. Thus, gating of normal epithelial chloride channels is regulated by both cAMP-dependent protein kinase and protein kinase C, and regulation by both kinases is defective in CF.     

Autonomic regulation of a chloride current in heart

In isolated heart cells, beta-adrenergic receptor stimulation induced a background current that was suppressed by simultaneous muscarinic receptor stimulation. Direct activation of adenylate cyclase with forskolin also elicited this current, suggesting regulation by adenosine 3',5'-monophosphate (cAMP). This current could be recorded when sodium, calcium, and potassium currents were eliminated by channel antagonists or by ion substitution. Alteration of the chloride equilibrium potential produced changes in the reversal potential expected for a chloride current. Activation of this chloride current modulated action potential duration and altered the resting membrane potential in a chloride gradient-dependent manner.     

An apical-membrane chloride channel in human tracheal epithelium

The mechanism of chloride transport by airway epithelia has been of substantial interest because airway and sweat gland-duct epithelia are chloride-impermeable in cystic fibrosis. The decreased chloride permeability prevents normal secretion by the airway epithelium, thereby interfering with mucociliary clearance and contributing to the morbidity and mortality of the disease. Because chloride secretion depends on and is regulated by chloride conductance in the apical cell membrane, the patch-clamp technique was used to directly examine single-channel currents in primary cultures of human tracheal epithelium. The cells contained an anion-selective channel that was not strongly voltage-gated or regulated by calcium in cell-free patches. The channel was also blocked by analogs of carboxylic acid that decrease apical chloride conductance in intact epithelia. When attached to the cell, the channel was activated by isoproterenol, although the channel was also observed to open spontaneously. However, in some cases, the channel was only observed after the patch was excised from the cell. These results suggest that this channel is responsible for the apical chloride conductance in airway epithelia.